Field of Art
The disclosure generally relates to the field of digital image and video processing, and more particularly to the implementation of color mapping and tone mapping within a camera architecture.
Description of the Related Art
Digital cameras capture images using an electronic image sensor. Example image sensors use CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) technology. For example, a CMOS image sensor contains photodiodes corresponding to pixels of a captured image. The captured image is presented in a RAW color space associated with the CMOS image sensor. The chroma, hue, and lightness of the captured image can be adjusted using color mapping after the image is captured by the camera. Color mapping maps the RAW color space to a target color space in order to achieve an accurate or preferred color reproduction for captured images. The adjustment to the chroma and hue can result in a less than desirable smoothness for various hues with varying chroma. Conventional color mapping methods adjust the chroma and hue using 3D look-up tables (“LUTs”) for chroma, hue, and lightness that are stored on the camera.
In addition to color mapping, tone mapping can play an important role in the capture, storage and reproduction of images because often the bit depth of the image's pixels has a limited dynamic range that is inadequate to capture all of the light intensities present in real-life scenes. Accordingly, tone maps specify which ranges of luminance are mapped to each bit value. General tone maps can be applied to images regardless of the content of the images. For example, tone map bit values may be allocated evenly across the luminance spectrum. However, tone maps can also be adapted based on image content to best represent the real-life scene captured in the image. For example, a scene that is dark or mostly shadowed may use a tone map that allocates more bit values to the darker end of the luminance spectrum than a tone map for an average scene. Similarly, a scene that is particularly bright or light may use a tone map that allocates more bit values to the lighter end of the luminance spectrum than a tone map for an average scene. However, when a scene contains both shadowed and bright features, application of a single tone map may compress features on either edge of the spectrum due to the limited bit depth of the tone map.
Accordingly, the optimization of color and tone mapping in such a way as to minimize undesirable artifacts and improve image quality is an important consideration in the capture of images and the subsequent color and tone rendering of the captured images.